1. Field of the Invention
The invention relates to fiber covered rolls used in the production of glass, aluminum or steel, and in other industries, for the purpose of conveying the product through a furnace, lehr, dryer or oven. The function of the roller may be to move the product without marking it, to prevent a thermal shock condition, or to eliminate "pick-up" of the conveyed material on the roller surface.
2. Description of the Prior Art
Conventional methods of fabricating these rollers formerly included the use of a metallic cylindrical mandrel on which asbestos discs are mounted and compressed, and then machined to be concentric. Health problems have caused asbestos to be replaced with other materials such as ceramic fibers, but these are sometimes undesirably brittle. Aluminum silicate fibers are available in the form of boards manufactured by a felting process. "Kaowool" and "Fiberfrax" are trademarks of such aluminum silicate fibers. The fibers are used with binders of the aluminum phosphate and/or silicon dioxide family, among others. A commonly used binder which is a colloidal silicon dioxide mixture is marketed under the trademark "Ludox", manufactured by the Dupont Company.
Among the problems of substituting aluminum silicate fiberboard directly for asbestos fiberboard is fiber breakage caused by brittleness of the dry aluminum silicate board when it is subject to compression, which may result in premature fiber failure. At elevated temperatures, a typical Ludox bound aluminum silicate fiber is also subject to shrinkage which may cause the fiber discs to become loose on the metal mandrel, creating relative movement and accelerated fiber damage.
Blom U.S. Pat. No. 3,763,533 shows a roller having a metal mandrel with a long monolithic fiber shell. This type of construction is unsuccessful because the monolithic fiber shell shrinks in all dimensions when exposed to elevated temperatures while the metal mandrel expands. When the shell shrinks in an axial direction while the metal mandrel expands, the shell may become loosened due to loss of end compression and rotate relative to the mandrel. It may crack or disintegrate due to large circumferential gaps being developed in a random manner. These "gaps" due to fiber shrinkage and mandrel axial expansion may consist of only a few large gaps across the full face of the roll covering. Large gaps may cause premature disc failure by allowing edge breakdown and disc separation and sideways collapse. Large gaps may also be objectionable in terms of product conveying. Furthermore, because of the ceramic-like characteristics of the bonded fiber shell, bending forces result in virtually no deflection, whereas the metal mandrel on which it is mounted will deflect. The result is that the ceramic shell is "milled out" in its central portion. At some point in time this milling will cause cracking, and the shell will begin to flop back and forth on the metal mandrel, resulting in additional wear. A catastrophic failure could occur in a relatively short period of time.
A search of the prior art has revealed the following pertinent U.S. patents:
Gaskell Pat. No. 1,930,999 PA1 Sherts Pat. No. 2,300,528 PA1 Lindquist Pat. No. 2,788,957 PA1 Keith Pat. No. 3,306,254 PA1 Goulding Pat. No. 2,501,629 PA1 Weber Pat. No. 1,883,183 PA1 Kitazawa Pat. No. 3,710,469 PA1 Gorman Pat. No. 3,853,525
In Gaskell Pat. No. 1,930,999 the roller has asbestos discs which may be compressed by the bolt 9 or the nut. However it does not show the features of the present invention.
In Keith Pat. No. 3,306,254 the washers 19 are held between end plates with a bolt 24 to compress the discs.
Goulding Pat. No. 2,501,629 was selected because it shows a roller using tie rods for holding the discs together, although in this structure there is an outer sleeve over the discs.
The remaining patents were selected as being of additional interest as they also relate to rollers with end pressure means or with discs on a mandrel.
In addition, my U.S. Pat. No. 3,815,197 relates to various means for forming rollers. U.S. Pat. No. 3,224,927 pertains to forming inorganic heat-resistant fiber material containing cationic starch and colloidal silica.